Secondary lithium cell

Abstract

A rechargeable current-generating cell is disclosed, composed of (a) an anode made of lithium or its alloys; (b) a non-aqueous electrolyte solution with a solid electrolyte or a molten electrolyte; and (c) a cathode of a vanadium-substituted alkali thiochromite having the general formula NayCrl-xVxS2, wherein x lies between 0.05 and 0.3 and y is 1 for the stoichiometric compound and from 0.1 to 0.4 for the non-stoichiometric one. The non-stoichiometric compound is obtained from the stoichiometric compound, by electrochemical oxidation thereof, either in the cell, after its assembly, or in a non-aqueous electrolyte solution in a separate vessel, prior to assembly of the cell. The non-stoichiometric compound can also be obtained by chemical oxidation of the stoichiometric one in a nonaqueous solution of iodine. The vanadium-substituted alkali thiochromite displays a substantially higher specific conductivity than the pure sodium thiochromite, whereby cathodes prepared with the new, substituted species can be discharged at higher current densities without reduction of energy density. Moreover, the open circuit voltage of the substituted species cathode is higher, resulting in a greater gravimetric energy density.

We claim: 
     
       1. A secondary lithium cell comprising an anode of lithium or its alloys, an electrolyte solution containing an ionizable lithium salt in a non-aqueous solvent in the liquid, solid or molten state, and a cathode of an alkali thiochromite, wherein part of the chromium of said thiochromite is substituted with another transition metal, vanadium, said substituted alkali thiochromate having the following general formula   Na.sub.y Cr.sub.1-x V.sub.x S.sub.2,     with   x being a numerical value from 0.1 to 0.2, and   y being equal to 1 for a stoichiometric compound, and a value from 0.1 to 0.3 for a non-stoichiometric compound.   
     
     
       2. The secondary lithium cell according to claim 1, wherein said cathode is prepared from said stoichiometric compound, and said stoichiometric compound then being oxidized electrochemically, to a value of y equals from 0.1 to 0.3, into said non-stoichiometric compound, in said cell after assembling of said cell. 
     
     
       3. The secondary lithium cell according to claim 1, wherein said cathode is prepared from said stoichiometric compound, and said stoichiometric compound is oxidized electrochemically, to a value of y equals from 0.1 to 0.3, into said non-stoichiometric compound, prior to assembling of said cell, in a non-aqueous electrolyte solution in a separate vessel. 
     
     
       4. The secondary lithium cell according to claim 1, wherein said cathode is prepared from said non-stoichiometric compound, said non-stoichiometric compound having been obtained by chemical oxidation of said stoichiometric compound in a non-aqueous iodine solution.